Stress levels over time in the introduced ascidian Styela plicata: the effects of temperature and salinity variations on hsp70 gene expression
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Species distribution, abundance, and long-term survival are determined by biotic and abiotic regimes. However, little is known about the importance of these factors in species range expansion. Styela plicata is a solitary ascidian introduced all over the world by ship fouling, including salt marsh habitats, where introduced populations must tolerate high seasonal variations in temperature and salinity. To determine the seasonal stress levels in a salt marsh population of S. plicata, we quantified heat shock protein (hsp70) gene expression using quantitative real-time PCR throughout a 2-year cycle. Results showed that hsp70 expression varied over time, with higher stress levels recorded in summer and winter. Periodic conditions of high temperatures, particularly when coupled with low salinities, increased hsp70 gene expression. Mortality events observed every year around June were concurrent with sharp increases in temperature (>6°C), indicating that drastic changes in abiotic factors may overwhelm the observed stress response mechanisms. Determining the ability of introduced species to cope with stress, and the thresholds above which these mechanisms fail, is fundamental to predict the potential expansion range of introduced species and design efficient containment plans.
KeywordsHsp70 Salinity Temperature Introduced species Ascidian Salt marsh
We thank Dr. A. Blanquer for providing the hsp70 sequences of S. plicata from Vilanova i la Geltrú and Blanes (Spain). We are in debt to Dr. B. Song for kindly hosting MCP in his lab at the Centre for Marine Science (UNC Wilmington) during part of this study. We thank the Genomics Unit of the Technical Services of the University of Barcelona and R. Seminago for their assistance running the real-time PCR. Dr. P. Erwin kindly reviewed the manuscript for English grammar. This research was supported by the Marie Curie International Reintegration Grant FP7-PEOPLE-2010-RG 277038 (within the 7th European Community Framework Program), by the Spanish Government projects CTM2010-22218 and CTM2010-17755, and by a University of Barcelona APIF fellowship to MCP.
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